Tools to compare antibody gold nanoparticle conjugates for a small molecule immunoassay

Antibody gold nanoparticle conjugates as recognition elements are essential for the overall performance of lateral flow assays. When immobilizing antibodies on gold nanoparticles, the challenge is to prevent aggregation and to ensure that the antibodies are correctly oriented so that they remain functional and their paratopes remain accessible. There are many methods available, and it is difficult to decide which one to use. To help selecting the most appropriate conjugate production method, different synthetic routes of binding antibodies to gold nanoparticles are systematically investigated for the purpose of a quantitative lateral flow test for small molecules. The direct comparison of different conjugate syntheses shows how to select a suitable conjugate for a lateral flow assay. The syntheses examined are direct adsorption of antibody, direct adsorption of reduced antibody, covalent binding to polyethylene glycol linker, and binding via biotin-streptavidin interaction. The conjugates are characterized using UV-Vis spectroscopy and dynamic light scattering to determine their stability. Their performance on structured lateral flow test strips is examined using calibrations for different amitriptyline concentrations. It was shown that the best conjugate for quantification of amitriptyline was realized by direct adsorption of an UV-light irradiated antibody to gold nanoparticles. The methods employed can serve as a guide for selecting the most appropriate conjugate for an application and enhance the performance of lateral flow assays.